EP2790849B1 - Planet for a planetary rolling-contact screw - Google Patents

Description

Planetary roller screw drives are increasingly being used in drive technology. A relative rotation between the spindle nut and the threaded spindle is converted into an axial displacement between the spindle nut and the threaded spindle. Between the threaded spindle and the spindle nut distributed over the circumference arranged planets are provided, which roll under the relative rotation of the threaded spindle and the spindle nut.

Out DE102010011819 A Planetenwälzgewindetrieb was known according to the features of the preamble of claim 1. The planet has a center section which is larger in diameter along its planet axis and has an end section of smaller diameter axially on both sides of the middle section, wherein a first engagement profile is formed on the lateral surface of the planet in the middle section and a second engagement profile is formed in the end sections. The planets are with their first engagement profile in rolling engagement with a helically wound around the spindle axis thread of the threaded spindle. The planets are with their second Eingriffseinprofil in rolling engagement with a nut-side engagement profile of the spindle nut.

The first engagement profile of the planets has a plurality of annularly arranged around the planetary axis first teeth, wherein between successive first teeth each have an annularly disposed about the planetary axis first groove for threaded engagement of the thread of the threaded spindle is formed, wherein the teeth of the central portion one Tooth contour is assigned. These first grooves are also referred to as feed grooves, because the rolling engagement with the threaded spindle allows the relative feed between the threaded spindle and the spindle nut. The second engagement profile has a plurality of ring-shaped around the planetary axis arranged second teeth, wherein between successive second teeth in each case an annular arranged around the planetary axis second groove is formed. These second grooves are also referred to as guide grooves because the planets are in rolling engagement with these second grooves are with the nut side engagement profile and are guided on a circular path around the spindle axis in the spindle nut.

During operation of the Planetenwälzgewindetriebes the planets can be acted upon with axial forces, which are transmitted via the engagement profiles between the spindle nut and the threaded spindle. If tooth tips break off on the teeth of the engagement profiles, proper operation of the planetary roller screw drive is disturbed.

The object of the invention was to provide a planet suitable for a Planetenwälzgewindetrieb planet, which avoids this disadvantage.

According to the invention, this object is achieved in that the two located at the ends of the central portion of the first edge teeth are formed within and spaced from the tooth contour of the first teeth of the central portion. The first teeth have a useful portion, which can be used for a Wälzeingriff with the threaded spindle. This useful portion extends from the tooth tip in the direction of the tooth root, but not up to a groove bottom of the groove, in which engages the thread of the threaded spindle. The useful portion extends over the overlapping region of the overlapping first teeth of the planets and the thread of the threaded spindle. The first edge tooth is arranged within this useful portion of the first teeth within and spaced from said tooth contour. The first edge tooth is thus underfilled with respect to the tooth contour of the first teeth. This underfill may extend from the tooth tip to the tooth root or the groove bottom of the adjacent groove so that the first edge tooth is completely formed within and spaced from the associated tooth contour.

The invention has recognized that a targeted reduction of the edge tooth, at least in the useful portion of the first teeth, contributes significantly to a perfect operation of the planetary roller screw drive. The first edge tooth is therefore not or not fully loaded in the rolling contact of the planet with the threaded spindle. The risk of marginal tooth failure is significantly reduced.

Sections of the tooth flanks of the invention according to the first edge teeth, which can not come into rolling contact with the threaded spindle due to the arrangement of planet and threaded spindle to each other, which are thus outside the Nutzabschnittes, can affect the first teeth associated tooth contour or pierced. Preferably, however, the first edge teeth may be disposed within the tooth contour associated with the first teeth and spaced therefrom, that is, from the tooth tip to the tooth root.

The rolling contact track may, viewed in longitudinal section through the planet, denote a point on the tooth flank, so that the rolling contact track forms an annularly closed line. The Wälzkontaktbahn can be seen as a line along the tooth flank seen in longitudinal section through the planet, so that the Wälzkontaktbahn denotes an annular closed surface. The rolling contact between the Wälzpartnern on the Wälzkontaktbahn can be punctiform or linear.

The deliberately made underfilling has particular significance in the forming manufacturing processes. When planets according to the invention are rolled in a rolling process, the rolling profile of the tool in the region of the first edge tooth is prepared accordingly. The planet blank to be formed in the rolling process may have a contour which is formed in the region of the first edge tooth to be formed in such a way that material of the planet blank is deformed in the free material flow and at least partially forms a contour of the first edge tooth. In this case, the rolling tool is not completely filled in the area of the first edge tooth, but there is room for a free material flow of material of the planet blank.

In particular, in a forming process for producing the planets, a suitable forming tool and underlying planetary blanks can be set up and matched so that the first edge teeth are formed within and spaced from the tooth contour of the first teeth. An inventive manufacturing method and an apparatus for carrying out the method are described below.

A plurality of teeth means that at least two teeth are formed, between which a groove is arranged. The teeth can limit the groove with their mutually facing tooth flanks. A tooth contour in the sense of the invention envelops the tooth; it describes the contour that properly produced first teeth have within the tolerances allowed.

In a known manner, the tooth flanks of the first teeth coaxially around the planetary axis arranged around first Wälzkontaktbahnen for the rolling engagement with a threaded spindle. The two intermeshing Wälzpartner touch each other in the rolling contact on the Wälzkontaktbahn which extends annularly around the planetary axis around.

In an embodiment according to the invention, the two first edge teeth of the middle section have a smaller tooth thickness than the other first teeth of the central section. This smaller tooth thickness is located on a radius of the Wälzkontaktbahn whose center lies on the planetary axis. In this way it is ensured that the first peripheral teeth are not or not fully loaded. Under load, the planets according to the invention, which are arranged in the planetary roller screw drive, can be subjected to a load by the threaded spindle, with elastic deformation of the components in rolling contact on their first edge teeth; However, the contour of the first edge teeth according to the invention ensures that the first edge teeth are loaded with a lower load than the other first teeth.

The tooth tips of the first edge teeth of the middle section are preferably arranged radially inside the tooth tips of the other first teeth of the middle section. This measure contributes to a reduced load on the peripheral teeth. A tooth height formed in the central portion from the groove bottom of the grooves to the tooth tip of the first edge tooth is preferably about 50% to about 90% of the tooth height of the other first teeth.

The second engagement profile of the end portion may comprise a plurality of annularly arranged around the planetary axis of the second teeth, wherein between successive second teeth in each case an annular around the planetary axis arranged second groove is formed. The annular and coaxial about the planetary axis arranged grooves and teeth may be parallel to a plane which is arranged transversely to the axis of the planet.

The end portion may have at its end facing the central portion of a second edge tooth, which is not fully formed as well as the first edge tooth. A tooth tip of the second edge tooth may be disposed radially inside the tooth tips of the other second teeth of the end portion. An undesirably high loading of the second edge teeth in rolling engagement with the spindle nut can be avoided with these planets according to the invention.

Neighboring adjacent first teeth may limit the first groove with their mutually facing tooth flanks, wherein adjacently arranged second teeth bound with their mutually facing tooth flanks, the second groove.

Between the central portion and the two end portions may be formed an intermediate portion which may extend in the axial direction from the tooth tip of the first edge tooth to the tooth tip of an adjacent second edge tooth of the end portion. The second teeth of the end portion are - relative to the planetary axis - smaller in diameter than the first teeth. The intermediate portion may advantageously taper along the axis of the planet in the direction of the end portion. In this way it is ensured that in the region of the intermediate portion only contact of the threaded spindle with the end portion facing tooth flank of the edge tooth is possible, a contact in the remaining intermediate portion is excluded.

At the free end of both end portions, a pin arranged coaxially with the planetary axis may be formed, the particular cylindrical surface of which may be arranged radially inside of tooth tips of the second teeth of the end portion. This pin, which is known per se on planets, serves to receive the planets in a cage. The pins engage in bearing openings of the cage and are rotatably mounted therein.

If planets according to the invention are produced without cutting in a forming process, for example in a rolling process, tooth tips of the edge teeth can be imperfectly formed; In the head region of such produced edge teeth, the tooth tip may represent a rugged surface, which has formed due to a free flow of material. The mutually remote tooth flanks of the first and second edge teeth can be properly formed under rolling contact with the rolling tool and can form a Wälzkontaktbahn.

The first edge tooth may be formed on its side facing the end portion with a partially formed tooth flank, which can come in rolling contact with the threaded spindle in the installed condition in Planetenwälzgewindetrieb under load and elastic deformation of participating components, although due to the inventively reduced first edge teeth the Main load is absorbed by the other first teeth of the middle section and the first edge tooth is loaded only heavily attenuated.

The second edge tooth of the end portion may have on its side facing the central portion no or only partially formed tooth flank. The inventive method described below for producing planets according to the invention enables economical production of planets that reliably ensure a connection between the spindle nut and the threaded spindle during operation.

First, a planetary blank is provided which has a thicker cylindrical central portion along its planetary axis and thinner cylindrical end portions located at both axial ends of the central portion, with a transition portion tapering from the central portion toward the end portion between the central portion and the end portion. This transition section may be designed conical. In the lateral surface of the planet blank, the first and the second engagement profile are rolled, wherein under a forming force, a lateral surface of the transition portion of the planet blank is formed in the free flow of material to an intermediate portion disposed approximately between tooth tips of the two adjacent first and second peripheral teeth of the central portion and the end portions is located.

Free flow of material means that the lateral surface of the transition section does not come into contact with a forming tool, and that the forming forces acting on both sides of the transition section on the raw planets, the transformation of the transition section to the intermediate section. The material of the raw planet is merely displaced in such a way to form the first and the second edge teeth, that the intermediate portion is formed. The transition section is dimensioned and arranged accordingly, it being ensured that the intermediate section - with the exception of the end section facing tooth flank of the first edge tooth - does not come into contact with the threaded spindle and the spindle nut of the planetary roller screw drive.

The forming forces acting on the planetary blank cause the transition portion of the planetary blank to be converted to the intermediate portion of the planet, with the intermediate portion extending in the radial direction between the tooth tips of the first and second peripheral teeth.

The transition section of the planet blank may have a conical circumferential surface, whose circumferential edge sections connect integrally to the cylindrical end sections and to the cylindrical central section. This conical lateral surface is arranged so that its deformation in the free flow of material produces the desired contour of the intermediate section.

The planetary blank can be produced in an economically favorable manner with its cylindrical central portion, its cylindrical end portions and its conical transition portions arranged between the central portion and the end portions by extrusion.

The extruded planetary blank can be ground in a subsequent grinding process, achieving a desired dimensional accuracy with close tolerances. Centerless grinding is ideal here.

During the forming of the planet blank, the two engagement profiles can be formed in the described manner and in addition the integrally connected at the free ends of the end portions pin can be formed. The pin diameter can be designed depending on the application and be smaller than the diameter of the groove bottom of the second grooves.

The planet produced in this manner can be hardened in a heat treatment process.

For the forming is particularly suitable for the rolling process, with the rotationally symmetrical body can be produced in an economically favorable manner. Rolling with flat jaw tools and rolling tools is suitable for the production of planets according to the invention. In the rolling process, rolling forces act on the planetary blank, which reshape the planetary blank in the desired manner as a forming force. Under a relative rotation of the roller burnishing rolls or a relative displacement of flat profiles provided with rolled profiles, the planetary blank clamped between the tool parts rotates and / or slides about its longitudinal axis, the planetary blank rolls and / or slides off the rolling profiles of the tool and the desired effect under the effect of the forming forces Contour is rolled into the planetary blank.

For carrying out the method according to the invention, in particular a flat jaw tool, comprising two flat jaws, which are each provided on their mutually facing sides with a rolled section for rolling in the two engagement profiles and the pins, wherein the two flat jaws are displaced along an axis relative to each other. The rolled section can have a middle rolled section for rolling in the first engagement profile, and an outer rolled section for rolling in the second engagement profile and the pins.

In the transition between the middle roll profile and the outer roll profile, a roll-free transition region can be formed without contact with the planetary blank. In this roller-free transition region, the transformation of the transition section of the planet blank takes place in the free flow of material, ie without the outer surface of the transition section in direct contact with the Rolling tool is. During the rolling process, the first edge tooth is not fully formed and is subjected to a free flow of material in its head region and its end region facing the tooth flank region.

The described Rohplanet allows economically favorable manner, the rolling of the first and the second engagement profile and the pin in a common rolling process.

Due to their economic production, planets according to the invention are particularly suitable for mass production, for example for the use of planetary roller screw drives in automobile construction.

Figur 1

einen erfindungsgemäßen Planeten,

Figur 2

eine Ausschnittsvergrößerung aus Figur 1,

Figur 3

ausschnittsweise einen Wälzeingriff zwischen einer Spindelmutter und dem erfindungsgemäßen Planeten,

Figur 4a

ein erfindungsgemäßes Flachbackenwerkzeug mit einem Planetenrohling vor einem Walzvorgang,

Figur 4b

das erfindungsgemäße Flachbackenwerkzeug aus Figur 4a mit einem gewalzten Planeten,

Figur 5

eine Ausschnittsvergrößerung aus Figur 4b,

Figur 6

einen erfindungsgemäßen Planetenrohling und einen für die Auslegung vorgesehenen Modellplaneten, jeweils in einem Halbschnitt, und

Figur 7

einen bekannten Planetenwälzgewindetrieb.

The invention will be explained in more detail with reference to an embodiment shown in a total of seven figures. Show it:

FIG. 1

a planet according to the invention,

FIG. 2

an excerpt from FIG. 1 .

FIG. 3

partially a rolling engagement between a spindle nut and the planet according to the invention,

FIG. 4a

an inventive flat jaw tool with a planet blank before a rolling process,

FIG. 4b

the flat jaw tool according to the invention FIG. 4a with a rolled planet,

FIG. 5

an excerpt from FIG. 4b .

FIG. 6

a planetary blank according to the invention and provided for the design model planet, each in a half-section, and

FIG. 7

a known Planetenwälzgewindetrieb.

FIG. 7 shows a conventional Planetenwälzgewindetrieb in which planets according to the invention can be used. A spindle nut 1 is arranged on a threaded spindle 2. Between the spindle nut 1 and the threaded spindle 2 planet 3 distributed over the circumference are arranged. At both axial sides of the planet 3 spacers 4 are arranged, which keep the planet 3 in the circumferential directions at a distance from each other. During operation, the planets 3 roll on the spindle nut 1 and on the threaded spindle 2 and rotate about their planetary axis. The spacers 4 rotate together with the planet 3 against the spindle nut 1 and the threaded spindle. 2

Each planet 3 has a center section 5, which has a larger diameter along its axis, and an axially smaller end section 6 on both sides of the middle section 5, wherein on the lateral surface of the planet 3 in the middle section 5 a first engagement profile 7 and in the end sections 6, respectively a second engagement profile 8 is formed. The planets 3 are with their first engagement profile 7 in rolling engagement with a helically wound around the spindle axis thread 9 of the threaded spindle 2. The planet 3 are with its second Eingriffseinprofil 8 in rolling engagement with a nut-side engagement profile 10 of the spindle nut. 1

The FIGS. 1, 2 and 3 Each planet 11 has a central portion 12 which is larger in diameter along its planet axis and an axially smaller end portion 13 on both sides of the central portion 12, respectively on, on the lateral surface of the planet 11 in the central portion 12, a first engagement profile 14 and in the end portions 13 each have a second engagement profile 15 is formed. The first engagement profile 14 is provided for a rolling engagement with a helically wound around the spindle axis thread of a threaded spindle. The second engagement profile 15 is provided for a rolling engagement with a nut-side engagement profile of a spindle nut.

The first engagement profile 14 of the planets 11 has a multiplicity of first teeth 16 arranged annularly around the planetary axis, wherein a first groove 17 arranged annularly around the planetary axis is formed between consecutive first teeth 16, the first teeth 16 of the central portion 12 in each case a tooth contour 18 is assigned. These first grooves 17 are also referred to as feed grooves, because the rolling engagement with the threaded spindle allows the relative feed between the threaded spindle and the spindle nut.

The second engagement profile 15 has a multiplicity of second teeth 19 which are arranged annularly around the planetary axis, wherein a second groove 20 arranged annularly around the planetary axis is formed between successive second teeth 19. These second grooves 20 are also referred to as guide grooves, because the planets 11 are provided with these second grooves 20 for a rolling engagement with the nut side engagement profile and are guided in a circular path around the spindle axis in the spindle nut.

Adjacent first teeth 16 bound with their mutually facing tooth flanks 21, the first groove 17th Adjacent second teeth 19 border with their mutually facing tooth flanks 22 to limit the second groove 20.

The annular grooves and teeth arranged annularly around the planetary axis described herein are arranged transversely to the axis of the planet.

At both axial ends of the planets 11 a coaxial with the planetary axis arranged cylindrical pin 13 a is provided for engaging in bearing openings of a spacer, as above to the FIG. 6 has been described.

The two located at the ends of the central portion 12 first edge teeth 23 are compared to the interposed other first teeth 16 in the inventive manner only imperfectly formed.

The two end portions 13 have at their the middle portion 12 facing ends in each case a second edge tooth 24, which is imperfectly formed with respect to the adjacent second teeth 19. The second tooth 19 facing the tooth edge 22 of the second edge tooth 24 is similar or the same design as the tooth flanks 22 of the adjacent second teeth 19. However, an intermediate portion 27 associated with other tooth edge 22a of the second edge tooth 24 is formed only imperfectly and not intended for a rolling engagement ,

Between tooth tips 25, 26 of the first edge tooth 23 and the second edge tooth 24, the intermediate portion 27 is formed. The tooth tip 25 of the first edge tooth 23 is due to their formation in the free flow of material only weakly formed. The second teeth 19 are based on the planetary axis in diameter smaller than the first teeth 16. The intermediate portion 27 tapers along the axis of the planet in the direction of the End section 13. The intermediate section 27 is dimensioned such that contact of the threaded spindle is possible only with the end section 13 facing tooth flank of the first edge tooth 23, a contact in the remaining intermediate section 27 is excluded. The intermediate portion 27 is not provided for the rolling engagement with the spindle nut.

The first teeth 16 have a parallel distance with an equal pitch t1. The second teeth 19 have a parallel distance with an equal pitch t2.

FIG. 2 clearly shows the first edge tooth 23 and adjacent one of the first teeth 16, the tooth tip 28 has a so-called closing fold 29 which is formed circumferentially around the planetary axis. The closing fold 29 is the result of a production process of the planet described below according to the invention. Significantly, the first tooth 16 associated tooth contour 18 is located, wherein the first edge tooth 23 is formed according to the invention within and at a distance from the tooth contour 18. The first edge tooth 23 is formed in this embodiment of its tooth tip to the groove bottom of the groove 17 within and spaced from the tooth contour 18.

The tooth tip 25 of the first edge tooth 23 is arranged radially inside the tooth tip 28 of the adjacent first tooth 16. The tooth height of the first edge tooth 23 is about 50-90 percent of the tooth height of the adjacent first tooth 16. At the tooth flank of the first edge tooth 23 facing the first tooth 16, the tooth height is 70 to 90 percent of the tooth height of the first tooth 16. At the second Edge tooth 24 facing tooth flank of the first edge tooth 23 is the tooth height to 50 to 70 percent of the tooth height of the first tooth 16. The tooth height extends from the groove bottom 20 a of the first groove 20th

With common planetary sizes up to about 10 mm in diameter, the first edge tooth of the middle section is about 2 times 0.005 to 2 by 0.02 mm narrower than the adjacent first teeth starting from a tooth center.

The surface of the first edge tooth 23 is formed in the area of the intermediate section 27 in the free flow of material; that is, due to plastic deformation of material of the planet, this surface has formed without the intermediate portion coming into contact with a forming tool.

With a radius w around the axis of the planet a Wälzkontaktbahn for rolling contact with a spindle nut is formed on the planet 11 in the central portion 12. In the amount of Wälzkontaktbahn a clear axial distance of the first edge tooth 23 is formed to the tooth contour 18. A rolling contact with the threaded spindle may be possible under elastic deformation of the load-transmitting components. However, the forces occurring in this rolling contact are significantly attenuated. The peripheral teeth are therefore not the starting point for damage.

FIG. 3 shows an enlarged detail of the planet 11 in the central portion 12 in rolling engagement with the threaded spindle 2. In the rolling contact K on the Wälzkontaktbahn the threaded spindle 2 and the planet 11 touch each other. It can clearly be seen that there is no rolling contact between the first edge tooth 23 and the threaded spindle 2. Only under further axial loading of the planetary roller screw thread rolling contact can occur due to elastic deformation; however, the force occurring in this rolling contact is the same low, that a breakout of material from the first edge tooth 23 is excluded. This advantage is given by the inventively underfilled first edge tooth 23.

FIG. 3 shows the engagement of the threaded spindle 2 in the grooves 17 of the central portion 12 of the planet 11. The thread of the threaded spindle 2 does not reach the groove bottom of the groove 17. Within the overlap of the thread of the threaded spindle 2 and the first teeth 16, the first teeth 16 on a useful section. In this exemplary embodiment, like first edge teeth 23 in the useful portion of the first teeth 16, within and at a distance from the tooth contour 18 (FIG. FIG. 2 ) and also arranged up to the tooth root, so to the groove bottom of the groove 17 within the tooth contour 18.

The FIGS. 4a and 4b show a flat jaw tool for producing planets according to the invention, wherein the method for producing the planets and the flat jaw tool for carrying out the method are described below.

The flat-jaw tool 30 has two mutually oppositely disposed flat jaws 31, which are each designed in three parts in the embodiment. The flat jaws 31 are each provided on their sides facing each other with a rolled section. The middle plate member 32 is provided with a middle roll profile 33 for rolling in the first engagement profile in the planets. The two outer flat jaw parts 34 are each provided with an outer rolled section 35 for rolling in the second engagement profile and the pins in the planets.

The flat jaws 30 extend out of the image plane along a tool axis, with the two flat jaws 30 being displaced relative to one another along this tool axis during the rolling process.

Between the two flat jaws 30, a planetary blank 11a is arranged, which in the rolling process to the planet 11 (FIG. Fig. 4b ) is rolled.

The planetary blank 11 a is produced in an economically favorable manner in the extrusion molding process. The extrusion is favored by the simple shape of the planetary blanks 11a, which has a cylindrical central portion 12a and two axially adjacent, non-stepped cylindrical end portions 13a. These non-stepped end portions 13a form after rolling the end portions and the stepped pins of the planets according to the invention. Between the end portions 13a and the middle portion 12a, a tapered transition portion 27a is formed, the axial edges of which connect integrally to the cylindrical ends of the central portion 12a and the end portions 13a. In the exemplary embodiment, the lateral surface of the conical transition section 27a encloses an angle of about 45 degrees with the planetary axis. After extrusion, the planetary blanks 11a are centerless ground and given a shape accuracy suitable for the subsequent rolling process.

For rolling, the two flat jaws 32 are driven towards each other, wherein the rolling profile of the flat jaws 32 pushes into the lateral surface of the planet blank and plastically deforms the planet blank. Under the tool movement, the planetary blanks 11a roll and slide against the flat jaws 32, the tool end being reached after several revolutions of the planet blank 11a, and the planet 11 having received its final contour.

Of the FIG. 4a It can be seen that the transitional portion 27a of the raw planet lies in a roll-free transition region of the flat-jaw tool 30, in which during the rolling operation, a contact of the transition portion 27a is excluded with the flat jaw tool.

FIG. 4b shows the finished rolled planet 11, as described in detail above. Significantly, a lens-shaped underfilled forehead of the planet 11 can be seen, which is shown in phantom. This lenticular underfilling is the result of the rolling process in the flat jaw tool 30 when the planetary blank has a flat end face. However, the lenticular underfill of the forehead can be suppressed with a suitably prepared face of the planetary blank.

During rolling material of the raw planet 11 a is formed and flows into the rolling profile of the tool. The contour of the rolled profile forces the flow of material into the intended contour of the planet, wherein due to the inventive design of the raw planet 11 a of the first edge tooth 23 is formed only on its the other first teeth 16 facing tooth flank by the rolling profile of the flat jaw tool. Otherwise, the edge tooth 23 forms in the free flow of material and is formed so small that during operation of a Planetenwälzgewindetriebes the first edge tooth 23 is not or only weakly loaded. Among the forming forces acting on the first and second edge teeth 23, 24, material of the raw planet 11 a is displaced in the region of the transition section 27 a.

FIG. 5 shows an enlarged detail FIG. 4b , Here it can be clearly seen that the transition portion of the planetary blank has been converted to the intermediate portion 27 of the planet 11, without contact with the rolling tool. This transformation takes place in the free flow of material. It can be clearly seen that the conical intermediate portion 27 tapers in the direction of the end portion 13. The flat jaw tool 30 is not filled in the region of the intermediate portion 27, it is created space for the free flow of material.

FIG. 5 By the rolling engagement of the middle rolled section 33, material of the raw planetary surface 11a is displaced radially outward between adjacent teeth of the rolled section to form the first tooth 16. The material flows in the direction of the tooth tip 28 Coming from both tooth flanks of the rolled section and opens into the tooth tip to form the closing fold 29th

FIG. 6 shows in half section a model planet 11b (top) and the planetary blank 11a (bottom) without the molded pins. The model planet 11b differs from the planet according to the invention only in that the edge teeth of the middle section are completely filled, that is not underfilled. With this model planet, the center distance from the one first edge tooth to the one can be other first edge tooth are specified. This center distance a is approximately in a further given relationship with the axial extent of the cylindrical central portion 12a of the raw planet 11a.

The center distance a is equal to or about the sum of the axial extent b of the cylindrical central portion 12a of the planetary blank 11a to the beginning of the 45 degree chamfer, plus ½ * t1 (half of the pitch t1). With this design, a planet 11 according to the invention can be produced with a shortened middle section and according to the invention underfilled edge tooth.

Planets according to the invention can thus be produced in an economical manner with the described flat-jaw tool in the manner described, wherein the raw planet is transformed into the planet in a single rolling process. The planet can then be hardened in heat treatment processes.

LIST OF REFERENCE NUMBERS

1

spindle nut

1

screw

2

planet

3

spacer

4

midsection

5

end

6

first intervention profile

7

second engagement profile

8th

thread

9

nut-side engagement profile

10

planet

11a

planet blank

11b

model Planet

11

midsection

12a

cylindrical middle section

12

end

13a

end

13

first intervention profile

14

second engagement profile

15

first tooth

16

first groove

17

tooth contour

18

second tooth

19

second groove

20a

groove bottom

20

tooth flank

21

tooth flank

22

first edge tooth

23

second edge tooth

24

tooth tip

25

tooth tip

26

intermediate section

27a

tapered transition section

27

tooth tip

28

closing fold

29

Flat baking tool

30

flat shoe

31

middle flat part

32

middle rolled section

33

outer flat part

34

outer rolled section

Claims (13)

1. Planet (11) for a planetary roller screw drive, along the planet axis of which a middle section (12) of greater diameter and, axially on both sides of the middle section (12), in each case one end section (13) of smaller diameter are configured, a first engagement profile (14) being configured on the circumferential face of the planet (11) in the middle section (12) and a second engagement profile (15) being configured in each case in the end sections (13), the first engagement profile (14) having a multiplicity of first teeth (16) which are arranged in an annular manner around the planet axis, in each case one first groove (17) which is arranged in an annular manner about the planet axis being configured between first teeth (16) which follow one another, characterized in that the two first edge teeth (23) of the middle section (12) which lie at the ends of the middle section (12) are configured within and at a spacing from a toothed contour (18) which is assigned to the first teeth (16) of the middle section (12).
2. Planet (11) according to Claim 1, in which tooth flanks (21) of the first teeth (16) have first rolling contact tracks which are arranged coaxially around the planet axis for the engagement of a threaded spindle, the two first edge teeth (23) of the middle section (12) having a smaller tooth thickness on a radius (w) of the rolling contact track around the planet axis than the other first teeth (16) of the middle section (12).
3. Planet (11) according to Claim 1, in which tooth tips (25) of the first edge teeth (23) of the middle section (12) are arranged radically within the tooth tips (28) of the other first teeth (16) of the middle section (12).
4. Planet (11) according to Claim 1, in which a tooth height which is configured in the middle section (12) from the groove bottom (17a) of the grooves (17) as far as the tooth tip (25) of the first edge tooth (23) is from approximately 50% to approximately 90% of the tooth height of the other first teeth (16).
5. Planet (11) according to Claim 1, in which the second engagement profile (15) of the end section (13) has a multiplicity of second teeth (19) which are arranged in an annular manner around the planet axis, in each case one second groove (20) which is arranged in an annular manner around the planet axis being configured between second teeth (19) which follow one another, an intermediate section (27) being configured between the tooth tips (25) of the first edge tooth (23) and a second edge tooth (24) of the end section (13) which lies closest to the middle section (12), which intermediate section (27) tapers along the planet axis in the direction of the end section (13).
6. Planet according to Claim 1, in which an intermediate section (27) is configured between the middle section (12) and the two end sections (13), which intermediate section (27) extends in the axial direction between the tooth tip (25) of the first edge tooth (23) and the tooth tip (26) of the adjacent second edge tooth (24).
7. Method for producing a planet according to Claim 1, according to the following steps:

   provision of a planet blank (11a) which has a thicker middle section (12a) along its planet axis and thinner end sections (13a) which lie at both axial ends of the middle section (12a), a transition section (27a) which tapers from the middle section (12a) in the direction of the end section (13a) being configured between the middle section (12a) and the end section (13a);

   rolling of the first and the second engagement profile (14, 15) into the circumferential face of the middle section (12a) and the end sections (13a), a circumferential face of the transition section (27a) of the planet blank (11a) being formed in the free material flow under a forming force into an intermediate section (27) of the planet (11), which intermediate section (27) lies between tooth tips (25, 26) of the two first and second edge teeth (23, 24) which are arranged adjacently with respect to one another.
8. Method according to Claim 7, in which the intermediate section (27) extends in the radial direction between the tooth tips (25, 26) of the first and the second edge teeth (23, 24).
9. Method according to Claim 7, in which the planet blank (11a) with the cylindrical middle section (12a), the cylindrical end sections (13a) and the transition sections (27a) which are arranged between the middle section (12a) and the end sections (13a) is manufactured by way of extrusion.
10. Method according to Claim 7, in which the extruded planet blank (11a) is ground in a subsequent grinding process.
11. Method according to Claim 9, in which the two engagement profiles (14, 15) and the journals (13a) which adjoin the free ends of the end sections (13a) integrally are rolled on the planet blank (11a).
12. Method according to Claim 11, in which the planet (11) is hardened in a heat treatment process after rolling of the engagement profiles (14, 15) and the journals (13a).
13. Apparatus for carrying out the method according to Claim 8, with a flat die (30), having two flat jaws (31) which are provided, on the sides which face one another, in each case with a rolling profile (33, 35) for rolling the two engagement profiles (14, 15) and journals (13a), the two flat jaws (31) being displaceable relative to one another, the rolling profile having a middle rolling profile (33) for rolling the first engagement profile (14), and an outer rolling profile (35) for rolling the second engagement profiles (15) and the journals (13a), and a roll-free transition region without contact with the planet blank (11a) being configured in the transition between the middle rolling profile (33) and the outer rolling profile (35).

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